1. Field of the Invention
The present invention relates to a method of manufacturing an optical component used by transmitting light through an inside thereof and an optical component.
2. Description of the Related Art
As a material of an optical component such as an optical low-pass filter for a CCD element or a CMOS sensor for, for example, a digital camera, for example, a chip-shaped quartz crystal has been used. This optical component uses a phenomenon such that a chip is cut off so that, for example, directions of crystal axes of a quartz crystal are parallel to a horizontal surface of the chip and the crystal axes incline only at a predetermined angle to four sides of the horizontal surface of the chip, and by making light incident vertically on the horizontal surface of this chip, the incident light is separated into two rays that are an ordinary ray in which the light incident on the chip is transmitted through the chip linearly and an extraordinary ray that is emitted parallel to this ordinary ray at a position away from the ordinary ray only at a predetermined distance. The position where this extraordinary ray is emitted on a rear surface side of the chip changes in accordance with, for example, an inclination angle of the crystal axes of the quartz crystal to the four sides of the chip.
Accordingly, for example, in a stack in which a plurality of quartz-crystal chips whose inclination angles of crystal axes are different from one another are stacked to be integrated, light is vertically radiated toward a stacking direction of the quartz-crystal chips, and thereby, when a single incident ray is transmitted through the first quartz-crystal chip, it is increased to two rays, and when these two transmitted rays are transmitted through the following quartz-crystal chip, they are increased to, for example, four rays in total because each of the transmitted rays is increased to two rays. Then subsequently, every time the transmitted ray is transmitted through the following quartz-crystal chip, the number of transmitted rays is increased. Therefore, it is possible to increase the number of paths of light transmitted through the stack, or to adjust an arrangement (a disposition) of the transmitted rays transmitted through the stack (the ordinary ray and extraordinary ray) in accordance with the number of quartz-crystal chips to be stacked or an inclination angle of crystal axes in each of the quartz-crystal chips. Thus, as for an optical component using this quartz crystal, the number of chips to be stacked in the stack, an inclination angle of crystal axes in each of the quartz-crystal chips and the like are adjusted in accordance with, for example, the number of pixels of an image sensor provided at a position where light transmitted through this stack is reached, a disposition of the pixels, and the like. Further, in order to adjust an optical path length, there is sometimes a case that an amorphous glass chip is interposed between these quartz-crystal chips, alternatively, glass chips whose respective optical characteristics such as, for example, a transmission region and a non-transmission region of light, are different from each other are bonded to each other to be stacked, and it is interposed between the quartz-crystal chips.
Therefore, this stack is composed of a plurality of layers whose linear expansion coefficients are different from one another since an angle of the crystal axes is displaced between the respective quartz-crystal chips as described above, or a glass plate having a physical property different from that of the quartz crystal is interposed between the quartz-crystal chips, or further a physical property is different even between the adjacent glass plates. A chip-shaped optical component made of such a stack is cut out from a substrate as below, for example.
To begin with, a stack 101 is formed as shown in FIG. 10(a) in a manner that as shown in FIG. 2 that will be described later, a plurality of substrates 103 that are made of a plurality of quartz crystals in which a direction of a crystal axis is parallel to a horizontal surface and an inclination angle θ to one side of a perimeter of the horizontal surface is different from one another, an amorphous glass, and the like and whose linear expansion coefficients are different from one another are adhered to one another by, for example, an acrylic adhesive 102. Then, as shown in FIG. 10(b), a cutting fluid such as, for example, a cooling water or a lubricating oil is applied to this stack 101, and the stack 101 is cut off in a grid manner with a whetstone 104 for cutting off by a process called dicing, and thereby rectangular quartz-crystal chips 100 are cut out from the stack 101. At this time, a large number of flaws called chipping are generated at upper and lower corner portions on a cut surface of the quartz-crystal chip 100 by the dicing process, and therefore, in order to suppress a size of this flaw and the number of flaws, this dicing process is performed in a manner that, for example, a speed (process speed) at which the whetstone 104 incises the stack 101 is set to be an extremely slow speed, which is, for example, approximately several mm/min. Thereafter, as for this chip, the cutting fluid and a cutting residue adhering to a surface thereof are removed by washing.
On the other hand, as a process method in which a chip is cut out from the substrate 103 composed of, for example, a single plate, besides the above-described dicing process, a process method called, for example, scribing has been known. Concretely, this process method is a method to manufacture the rectangular quartz-crystal chip 100 in a manner that as shown in FIG. 11(a), for example, firstly, for example, a sharp diamond cutting edge 105 or the like is pressed against a surface of the substrate 103, and as shown in FIG. 11(b), a linear crack is formed in a grid manner along an outer edge of a chip, and next, as shown in FIG. 11(c), by adding loads to the substrate 103 and propagating this crack in a thickness direction of the substrate 103, the substrate 103 is cut off, and as shown in FIG. 11(d), the substrate 103 is split (broken).
In this process method, the process is easy to be performed since only the crack is formed in the surface of the substrate 103 in the process performed by the diamond cutting edge 105, and therefore it is possible to run the diamond cutting edge 105, for example, approximately several tens times faster than the whetstone 104, and therefore to perform the process faster than the already-described dicing process. Accordingly, productivity is improved more than that of the dicing process, and the number of process apparatuses is also reduced. Further, the scribing process is performed only in a manner that the substrate 103 has the crack formed in the surface, thereby being cut off into chips as described above, so that it is possible to suppress a size of a flaw and the number of flaws more than the dicing process. Further, a cutting fluid is unnecessary for this scribing process, so that it is possible to simplify washing of the chip after being processed and processing of a waste liquid.
Thus, it is desirable that the above-described stack 101 is also processed by this scribing. However, this stack 101 has the adhesive 102 to be a buffer material interposed between the respective substrates 103 and 103 as described above, and this adhesive 102 does not cause a brittle fracture, so that the propagation of the crack from an upper layer is obstructed. Therefore, as shown in FIG. 12, the crack is not easily reached at the substrate 103 on a lower layer side as it goes toward the substrate 103 on the lower layer side, and it is difficult to cut off this stack 101.
On the other hand, as disclosed in Patent Document 1, for example, there has been known a method in which the plural substrates 103 are bonded directly without such an adhesive 102 interposed therebetween. This method is a method in a manner that a molecule including, for example, oxygen (O), hydrogen (H), and the like is interposed between the substrates 103 and 103 to be heated at, for example, approximately 400° C., and thereby the plural substrates 103 are bonded with strong cohesion between the molecules. This method is considered to enable the crack to be formed integrally in the stack 101 by the scribing because the adhesive 102 is not interposed between the substrates 103 and 103. However, this stack 101 is composed of the plural substrates 103 whose linear expansion coefficients are different respectively as described already, and a proportion of which the substrate 103 expands and shrinks by heating and cooling at bonding differs in each of the substrates 103, and therefore, there arises a case that a break is caused in the substrate 103 at bonding processing, or the substrates 103 cannot be bonded.
In Patent Document 2, there has been disclosed an art in which when directly bonding two substrates having different linear expansion coefficients, a substrate having substantially the same linear expansion coefficient as that of the substrate on one side is interposed between the two substrates, but this method makes the stack 101 extremely thick.
[Patent Document 1] Japanese Patent Application Laid-open No. 2006-248895 (paragraphs (0113) to (0126))
[Patent Document 2] Japanese Patent Application Laid-open No. Hei 07-086106 (paragraphs (0008) and (0009))